1. Field of the Present Invention
The present invention relates generally to automated control of construction equipment, and, in particular, to the use of geodetic devices and information derived therefrom to automatically control, in three dimensions, the operation of slip form paving equipment and other construction equipment.
2. Background
In the construction industry, a longstanding issue has been how to accurately determine, on the construction site, the desired location for a building, road or other construction project as specified in plans developed by an architect, engineer, or the like. Most commonly, surveying techniques, supplemented in recent decades by advances in surveying technology, have been used to pinpoint and mark precise locations on a construction site, thereby guiding construction workers as they work.
Unfortunately, during construction, the locations marked by the surveyors may be affected by the construction process itself. For example, stakes that are laid out by surveyors to mark the edges of a planned road may be moved, covered or destroyed by earth-moving equipment as excavation, fill or the like is carried out. As a result, construction must often be halted temporarily while surveyors reestablish the construction locations, and the earth-moving process is continued.
More recently, advances in global positioning system (“GPS”) technology have begun to find applicability in the construction industry. Perhaps most obviously, GPS technology is now widely used by surveyors because it permits actual physical locations to be determined with accuracy to the nearest hundredth of a foot. Because the plans for most construction projects today are developed via computer, such techniques are particularly useful because the plans can be coordinated with the GPS data, thereby providing precise guidance during the surveying process.
In addition, however, GPS has begun to be used to guide the operation of construction equipment during the construction process itself. In fact, the use of so-called three-dimensional (“3D”) controls to direct the operation of construction equipment is becoming increasingly common, particularly with regard to earthmoving equipment. A typical implementation of a 3D control system in such a context involves the use of one or more fixed base stations, located in and around the construction site, coupled with one or more mobile units respectively disposed on the various pieces of construction equipment that are to be controlled via the system. As described below, the type of control system used may vary, but in each case, the exact position of each base station may be established by conventional surveying means, optionally supplemented by the use of GPS technology.
In one type of 3D control system, the mobile unit is a GPS unit, and thus the position of the mobile unit, and indirectly, the construction equipment on which it is carried, may be determined with some accuracy using only the mobile unit. However, in this arrangement, the GPS data developed by the mobile unit may be supplemented and adjusted, as appropriate, using additional location data from the fixed base stations, the position of each of which is known with great accuracy. This, in turn, provides highly accurate information about the exact position of the mobile unit, and indirectly, the construction equipment. Of course, as is well known, a stationary GPS unit, by itself, can not directly indicate any direction or orientation.
More commonly, however, the base station is a robotic laser-based tracking station, sometimes called a “total station,” and the mobile unit is a prism, wherein the robotic tracking station produces one or more lasers and directs them toward the construction equipment, and more particularly, toward the prism, which is mounted in a prominent location on the construction equipment to maximize its ability to receive the laser. In this type of 3D control system, the laser is used to determine the position of the prism relative to the base station by calculating distance and angle. Because the position of the base station is known, the position of the prism, and indirectly the position of the construction equipment, may be established using the combination of the fixed location information developed or known by the base station (which may or may not utilize GPS information) and the relative positional information provided using the laser and prism.
Unfortunately, the use of prisms creates a number of complications. First, in order to maintain line-of-sight between the prism and the robotic tracking station, the prism is usually elevated above what it is measuring or controlling. As a result, the center of the prism usually cannot be physically held at the point you want to measure or locate. Thus, because the point being measured is always offset from the center of the prism, manual point location is currently achieved by placing the prism on a pole, of known length, and then by aligning and hold the poll plumb to the earth. This process, although very common, is time consuming and is prone to operator error.
Further, like a GPS device, a prism can only be used to locate a single XYZ point in space. A stationary prism, by itself, thus can not directly indicate any direction or orientation.
Still further, a robotic tracking station can only track one prism at a time. Using multiple prisms (e.g., two or three) will allow direction (using two prisms) or orientation (using three prisms) to be determined, but doing so requires additional robotic stations to be setup and calibrated.
Regardless of which type of system is used to determine it, position by itself is not sufficient to control the operation of the equipment. For example, steering a mobile machine further requires knowledge of the machine's orientation in two-dimensional space. Conventionally, the machine's orientation is determined indirectly as being closely related to the machine's direction of travel. Currently, determining a machine's travel direction involves comparing the machine's current location, determined via one of the previously-described systems, to its previous location. The vector defined by those two points approximately defines the machine's current direction of travel.
Unfortunately, this approach includes a number of inherent inaccuracies. First, this approach is dependent upon sufficient movement by the machine in a straight forward direction. The approach cannot work at all if the machine is not moving, because direction of travel cannot be determined in this way if the current location and the previous location are the same. Further, the approach may be highly inaccurate if the current location and the previous location are particularly close to each other, which may happen if the machine is operating in a confined area or is of a type that can spin in place or turn with a very tight turning radius.
For example, FIG. 1 is a plan view illustrating the path of a reference point 2, such as where a prism is likely to be mounted, on a conventional slip-form curbing machine 10 that is being used to form a curb 40 having a curved section of uniform radius. As the curbing machine 10 moves along the ground 12 in the direction of travel indicated by the arrows 14, the reference point 2 first follows a straight path that is substantially parallel to the course of the straight curb 40 being formed (i.e., the section of curb 40 shown at the bottom of FIG. 1). However, the path 4 of the reference point 2 begins to diverge from the course of the curb 40 when the curb begins curving. In particular, the path 4 of the reference point remains straight for a significant distance before its curvature begins to match that of the curb 40 itself. Notably, the effective distance between the path 4 of the reference point 2 and the course of the curb 40 is significantly greater along the curved section of the curb 40 than along the straight sections of the curb 40. When the curb 40 straightens out again, the reference point path 4 must thus make an adjustment to return to the lesser spacing that exists along straight sections of the curb 40. Overall, then, the dissimilarities between the path 4 of the reference point 2 and the course of the curb 40 in FIG. 1 thus graphically illustrate the inherent difficulty of tracking and controlling a construction machine 10 using a single reference point 2 on that machine 10.
Although not illustrated in FIG. 1, another inaccuracy stems from the fact that machine orientation is not exactly equivalent to direction of travel. For example, it is impossible to determine precisely whether the path traveled by the machine from its previous location to its current location followed a straight line or a curved one. The orientation of the machine at the current location will be different if the machine followed a straight line to get there than if it followed a curved one.
Yet another inaccuracy stems from the use of positional data for only a single point (the point at which the mobile unit is positioned on the machine) to represent the position of the entire machine. In fact, most machines are several meters wide, several meters long and at least a couple of meters high. Because GPS (coupled with one of the systems described above) may be used to determine location to accuracies of considerably less than a meter, the positional data thus determined is accurate only for a small part of the machine, i.e., the exact location of the mobile unit on the machine. The position or location of other parts of the machine, such as the machine's operational components, may be determined only by combining information about the relative disposition of the mobile unit on the machine with knowledge of the geometry of the machine. For machines whose typical use involves travel only in a linear direction, and deviations from such travel occur only infrequently, this approximation may be acceptable. However, for other types of machines that turn regularly, or whose operational components move or are adjusted dramatically relative to the rest of the machine (for example, excavator shovels), the error induced between the fixed position of the mobile unit and the position or orientation of the operational components can become dramatic, thus rendering the use of such a system unsuitable for controlling certain types of machines.
The significance of this problem increases in relation to the degree of independence with which the operational components of the machine move relative to the movement of the machine itself. For example, in a curbing machine, the slip forming equipment mounted on the machine is typically adapted to form curbs having very short radiuses of curvature while the machine itself moves forward or stops altogether. In such a process, the movement of the operational components is thus very different from the movement of the machine itself. Conventional 3D control systems are ill-equipped to address this issue.
Paving and curbing equipment further require the attitude of the machine side-to-side (generally referred to as “cross slope”) and the attitude of the machine front-to-back (generally referred to as “long slope”) to be accurately controlled in order to maintain the proper three-dimensional form (side-to-side and front-to-back) of the pavement or curbing being formed. Traditionally, the machine location, direction, and long slope is referenced from a string line, as better described below, that is placed ahead of time to guide the location of the slip-forming equipment on the machine, while cross slope is monitored by a cross slope sensor. To better illustrate this and other limitations of conventional 3D control systems with regard to paving apparatuses, the following description of a conventional paving apparatus is presented, wherein FIG. 2 is a perspective view of a conventional slip form paving apparatus 10 such as is illustrated schematically in FIG. 1. The paving apparatus 10 is illustrated in FIG. 2 traveling over a ground surface 12 in the direction indicated by the arrow 14. The paving apparatus 10 comprises a main frame 20 supported substantially horizontally on a plurality of ground engaging members 22. Often, a single front ground engaging member 22, which is steerable, and a pair of rear ground engaging members 22 are mounted to the main frame 20 in a triangular relation to each other to provide stable suspension of the frame 20 in a generally horizontal position above the ground surface 12.
A mold 32 having a desired cross sectional shape corresponding to the cross sectional shape of the structure to be formed, such as a curb and gutter structure, is supported by the frame 20 and positioned on one side of the paving apparatus 10 to facilitate continuous slip forming of a concrete curb and gutter such as are typically formed along the sides of a roadway during road construction. The paving apparatus 10 also includes a hopper 34 and a conveyor 36. Together, the conveyor 36 and hopper 34 are adapted to receive concrete or other flowable paving material 38 from a separate paving material supply (not shown) and to convey the flowable paving material 38 to the mold 32. Flowable paving material 38 is continuously supplied to the mold 32 such that a continuous paving structure 40 is formed on the ground surface 12 as the paving apparatus 10 moves along the ground.
The ground surface 12 on which the paving structure 40 is to be laid in molded form is typically prepared in advance by suitable construction grading equipment. At least partially because of the problems described above, it is common practice during such preparations to construct an external datum from which the position of the curb or other paving structure can be determined. Typically, the external datum used consists of a string line 16 supported by a plurality of line holders 18, each of which includes a stake and a rod. Using an external datum such as a string line has traditionally proven advantageous because paver operations may be automatically controlled using various sensors for determining the position of the paving apparatus 10 relative to the string line 16.
Specifically, the paving apparatus 10 is often provided with a steer sensor 42, front grade sensor 46, rear grade sensor 48, and a slope sensor 49 (shown in FIG. 3). The steer sensor 42 and grade sensors 46,48 are neutral or “null” seeking, and each may be either a contact type sensor having a wand contacting the string line or a non-contact type sensor such as those using ultrasonic ranging or other non-contact sensing technologies. As illustrated in FIG. 2, the steer sensor 42 includes a steer sensor wand 44 and the front and rear grade sensors 46,48 include grade sensor wands 50. It should be noted that the steer and grade sensors 42,46,48 may be mounted on the paving apparatus 10 in a manner that allows the sensors to be horizontally and vertically adjustable relative to the paving apparatus 10. The mounting apparatus used, however, typically allows for the position of the steer and grade sensors 42,46,48 to be fixed relative to the paving apparatus 10 during paving operations.
The paving apparatus 10 is positioned on the ground surface 12 upon which the paving structure 40 is to be laid in such a manner that the mold 32 is located relative to the string line 16 in the position that the paving structure 40 is desired to be laid. The steer sensor wand 44 and grade sensor wands 50 are in contact with the string line 16 such that the wands are tangent to the string line 16. Generally, it is preferable to use two grade sensors 46,48, one on the front of the frame 20 and one on the rear of the frame 20. Each steer and grade sensor 42,46,48 produces an electrical output signal in proportion to the deflection of its respective wand from the neutral or null position. Preferably, a slope sensor 49 is located on the paving apparatus 10 to detect changes in cross slope as the apparatus 10 travels over the ground 12 and to generate an output signal proportional to the change in cross slope detected. Slope sensors may be, but are not required to be, of the dampened pendulum type.
The main frame 20 of the paving apparatus 10 is supported on the ground engaging members 22 by a plurality of posts, which are independently extendable or retractable to vary the position of the main frame 20 with respect to the ground engaging members 22. Because the mold 32 is also supported by the main frame 20, changing the position of the frame 20 changes the position of the mold 32 as well. The posts are typically operated by hydraulic piston-cylinder mechanisms 52,54,56 or, alternatively, the posts may be threaded posts that are rotated by associated reversible hydraulic motors. Three such piston-cylinder mechanisms are illustrated in FIG. 2, including a front grade piston-cylinder mechanism 52, a rear grade piston-cylinder mechanism 54, and a slope piston-cylinder mechanism 56. The front grade piston-cylinder mechanism 52 illustrated in FIG. 2 is supported by a ground engaging member 22 that includes a hydraulically operated steering mechanism, which may be a piston-cylinder mechanism or a hydraulically operated threaded post mechanism, that rotates the ground engaging member 22 relative to the front grade piston-cylinder mechanism 52 to thereby steer the paving apparatus 10.
Automatic paving operations may be conducted using the sensors 42,46,48 and piston-cylinder mechanisms 52,54,56 described above. After the paving apparatus 10 and sensors 42,46,48 are correctly positioned relative to the string line 16, paving apparatus 10 travel and paving operations may commence. When deviations in the horizontal direction of paving apparatus 10 travel are detected by the steer sensor 42, the steer sensor 42 generates an output signal used to operate a steering servo valve, which directs hydraulic fluid to the appropriate port on the steering mechanism in order to turn the steerable ground engaging member 22 in the direction required to return the steer sensor wand 44 to its neutral or null position. The paving apparatus 10 may further include an additional sensor (not shown) to measure the steered angle of the ground engaging members 22. The steering sensors command a proportional steered angle wherein the ground engaging member 22 steers and then remains at a fixed angle relative to the steering sensor.
Similarly, deviations in the vertical direction of the main frame 20 relative to the string line 16 are detected by the front and rear grade sensors 46,48 each of which generate an output signal used to control a servo valve associated with the front grade piston-cylinder mechanism 52 and the rear grade piston-cylinder mechanism 54, respectively. The piston-cylinder servo valves control extension or retraction of their associated piston-cylinder mechanisms 52,54,56 to return the frame 20 to a position in which the front and rear grade sensors 46,48 are in their null position.
Changes in mold cross slope as the paving apparatus 10 travels are detected by the slope sensor 49, which generates an output signal used to control a servo valve associated with the slope piston-cylinder mechanism 56, located on the opposite side of the frame 20 from the string line 16. Extension or retraction of the slope piston-cylinder mechanism 56 is used to change the position of one side of the frame 20 in order to compensate for changes in ground slope or to induce a desired cross slope on the mold 32. Although only one slope piston-cylinder mechanism 56 is shown in FIG. 2, additional slope posts or piston-cylinder mechanisms may also be used.
Typically, a pulse pickup device (not shown) is installed on the hydraulic motor of a driven ground engaging member 22 to generate a signal used to a determine the distance the paving apparatus 10 travels and the speed of the travel of the paving apparatus 10.
Proper control of the paving apparatus 10, and particularly of the mold 32, depends on proper determination and use of a variety of geometric relationships. For example, in many applications, it is desirable for slip form pavers to control the mold position during paving operations such that the cross slope of the mold is changed as the paving apparatus 10 travels along the string line 16 to thereby produce a paving structure 40 having a variable cross slope. Put another way, the paving apparatus 10 travels along a ground surface 12 that has a cross slope, and the paving apparatus 10 is capable of positioning the mold 32 with respect to the ground surface 12 such that the mold 32 itself has a cross slope.
Determination of the proper mold position is conventionally dependent on the determination of the current and/or proper mold position relative to the string line 16. FIG. 3 is a schematic diagram illustrating the relationship between the mold 32, the string line 16, and the control system sensors for the conventional paving apparatus 10 of FIG. 2. The value or angle of the cross slope for a particular mold is the value of the angle formed between the ground surface 12 and an imaginary reference plane 58 enclosing the bottom of the mold 32, when viewed in the transverse direction relative to the paving apparatus' direction of travel 14. Whenever it is desired to extrude a paving structure 40 having a transverse angle equal to the slope of the ground surface 12, then there would be no cross slope on the mold 32 for use in forming the given structure 40. In other words, the mold 32 would be level relative to the ground surface 12.
The determination of proper mold position is even more complicated in those applications in which it is desirable to form a paving structure 40 having a cross slope that is different from the slope of the ground surface 35 onto which the structure is laid. For example, it is often desirable when making gutters or curb and gutter structures 40 to form the gutter pan with either a “catch” or “spill” angle as previously described. Transitioning between an initial mold cross slope and a desired or altered mold cross slope during paving apparatus 10 travel along the string line 16 can be accomplished automatically as described, for example, in commonly-assigned U.S. Pat. No. 6,109,825, the entirety of which is incorporated herein by reference. In FIG. 3, the mold 32 is shown in a paving operation in which the ground surface 12 has zero slope and in which there is no cross slope on the mold 32. The steer sensor wand 44 and the grade sensor wand 50 are in contact with the string line 16 and the mold 32 is adjacent the ground surface 12 in a position relative to the string line 16 in which it is desired to form a curb and gutter structure 40. An imaginary control line 62 extends between the string line 16 and the slope sensor 49. Notably, the slope sensor 49 is illustrated only schematically in FIG. 3; this illustration does not therefore attempt to show the position of the pendulum in the slope sensor 49 at a given time. The desired location of the mold 32 relative to the string line 16 is measured as the distance, broken into a vertical mold distance (“VMD”) and a horizontal mold distance (“HMD”), between the string line 16 and a predetermined reference point 60 on the mold 32. Where the mold 32 is a curb and gutter mold, the predetermined reference point 60 on the mold 32 is often the intersection of the back of curb (“BOC”) and the top of curb (“TOC”). A cross slope may be established by extending or retracting the slope piston-cylinder mechanism 56. The extension or retraction of slope piston-cylinder mechanism 56 causes rotation of the mold and control sensors around the control string line 16, illustrated by double-pointed dotted lines in FIG. 3. For example, a cross slope may be established by extending the slope piston-cylinder mechanism 56, in which case the reference point 60 on the mold 32 moves up and to the right along the arcuate path illustrated in FIG. 3. The magnitude of the movement of the mold 32 in the horizontal and vertical directions may each be caused calculated as a function of the cross slope angle. Unfortunately, the extension or retraction of the slope piston-cylinder mechanism 56 causes numerous downstream interrelated effects that must be managed. Some of these problems, and one possible solution therefor, are discussed in the aforementioned '825 patent.
Solutions such as those described in the '825 patent, however, are dependent upon the use of a conventional string line 16 to control the paving apparatus 10. If a 3D control system of one of the types described hereinabove is applied to such equipment, the only information continuously established with regard to the machine is the location of the single mobile unit (most often, a prism); all other information must be extrapolated, with varying degrees of accuracy, or must be developed using other means. For example, the determination of long slope for the equipment requires an additional sensor over and above the cross slope sensor. Such a sensor is not usually provided on string line-controlled machines, and thus represents an additional complication in the application of conventional 3D control systems to, for example, paving and curbing machines.
Not to be ignored is the traditional importance of the string line 16 in establishing, indirectly, the location of other features as well. Conventionally, the string line 16 is one of the first construction elements put in place on a construction site. Other construction elements are either placed based directly on the string line 16 or are placed based on the paving structure 40 that is built by the paving apparatus 10.
In view of all of the foregoing, a need exists for a 3D control system for construction equipment, particularly paving and curbing equipment, that may be used reliably to guide the operation of such equipment. Such a control system needs to be able to determine geodetic information about the equipment, including its location, direction and orientation, with sufficient accuracy to be relied on to replace the use of string lines 16 and other technology in the construction environment.